Radiation deflecting systems employing counterrotating wedges, or prisms, adapted for use with various types of radiation subject to refraction are well known. For example, a scanning antenna utilizing four rotary prisms for use in a radar system is shown in U.S. Pat. No. 3,226,721 by R. V. Gould. Optical scanning devices, for use with light radiation, are shown in U.S. Pat. Nos. 1,647,631 and 2,975,668 by H. E. Ives and A. F. Eckel, respectively, and an acoustic imaging and image deflection system similar to the present disclosure is shown in the U.S. Pat. No. 3,913,061, issued Oct. 14, 1975, by Philip S. Green and assigned to the same assignee as the present invention, the subject matter of which patent specifically is incorporated herein by reference.
With many prior art arrangements a pair of counterrotating wedges are mounted in axial alignment and rotated in opposite rotational directions at the same rate of rotation whereby the wedges, located in the path of radiation, deflect the radiation to effect a generally linear scanning motion in one direction. For simultaneous image focusing and deflection a lens system is employed in conjunction with the deflecting means whereby the entire image is scanned or deflected. Problems of image distortion, radiation loss, and multiple internal reflections are encountered with such prior art arrangements. In particular, the angle of incidence at one or more of the refracting surfaces included in the system often is large whereby critical angle reflection, mode conversion (in the case of acoustical energy), aberration, and other such deleterious effects and phenomena are encountered or exacerbated by operation with large incident angles.